De-oiling method

ABSTRACT

An apparatus for use in de-oiling components comprises a furnace (10) for receiving components to be de-oiled and pumps (12, 14, 16) for creating a vacuum in the furnace. At least one of the pumps is a liquid ring pump. Oil is utilised to form the liquid ring and the oil is selected to be compatable with or the same as the oil to be removed from the contaminated components.

This invention relates to an apparatus and a method for use in de-oilingcomponents.

In industry, assemblies of pressings, such as evaporators, radiators,air-conditioning units and the like are formed of layers of aluminiumalloy strips which have been brazed together. During pressing, thestrips are often contaminated with the oil used to lubricate the pressesand such oil must be removed prior to the brazing operation takingplace. In the past, this de-oiling was carried out using solventshowever, due to environmental concerns, use of such solvents is nowdiscouraged.

One recently introduced method of de-oiling such components involvesheating the contaminated components to temperatures between 250° C. and350° C. in a vacuum furnace. The vacuum is achieved through use of Rootsblowers and rotary piston pumps. However, this arrangement hasencountered numerous problems including the relatively low viscosity oilbeing removed from the components condensing in the piston pump andeither causing the pump to seize, due to the thinning of the pumplubricating oil, or the loss of vacuum due to the relatively high vapourpressure of the press lubricating oil. In order to minimise theseproblems, cryogenic condensers have been provided between the furnaceand the piston pump with the intention that the oil vapour will betrapped in the condenser, and thus will not contaminate the pump. Inpractice, such condensers are only 80% efficient and a considerablequantity of oil still reaches the piston pump.

Further, there are a number of risks associated with the use of suchvacuum furnaces. In particular, if any oil droplets remain in thefurnace there is a risk that these will ignite, and cause an explosion,when the hot furnace is opened to remove the de-oiled components.

It is among the objects of the embodiments of the present invention toobviate and mitigate these disadvantages.

According to the present invention there is provided apparatus for usein de-oiling components, the apparatus comprising:

a furnace for receiving components to be de-oiled; and

means for creating a vacuum in the furnace, said means including aliquid ring pump, wherein oil is utilised to form the liquid ring andthe oil is selected to be compatible with or the same as the oil to beremoved from the components.

According to a further aspect of the present invention there is provideda method of de-oiling contaminated components, the method comprising thesteps:

heating the oil-contaminated components in a furnace;

pulling a vacuum in the furnace using a liquid ring pump utilising oilto form the liquid ring; and

selecting the oil utilised to form the liquid ring for compatibilitywith the oil to be removed from the components.

As used herein, the term "oil" is intended to encompass oils, greasesand the like as may be used for lubrication and cooling of machinery,tools and components.

In use, the invention allows the vaporised oil from the componentsheated in the furnace to condense within the pump, or in the pipeworkleading to the pump, without adversely affecting the operation of thepump. Any excess oil collecting in the pump is simply drained away fordisposal or separation and re-use. Thus, the need to periodicallyreplace "contaminated" pump oil is obviated. Also, apparatus necessaryfor condensing the vaporised oil before it reaches the pump, such as thecryogenic condensers provided in conventional systems having rotarypiston pumps, may be omitted, providing a significant saving in plantcosts: a simple heat exchanger\condenser may be provided on the pumpexhaust to condense any oil vapour which passes through the pump.

Preferably, the system includes lobed pumps, most preferably one or moreRoots blowers. As the operation of these pumps is unaffected by thepresence of oil vapour in the air being drawn from the furnace suchpumps may be provided between the liquid ring pump and the furnace. Mostpreferably, these pumps are vertically spaced to minimise collection ofcondensate therebetween.

Preferably also, the furnace is provided with heating means spaced fromthe walls of the furnace chamber, to facilitate cooling of the heatingmeans and the components at the end of a de-oiling cycle, before openingthe chamber: if the furnace temperature is high on opening the chamberthere is a risk of explosion through ignition of any oil remaining inthe chamber. It is further preferred that the furnace chamber, and thecomponents therein, are cooled by venting the chamber at the end of thecycle. Preferably, the chamber is vented with an inert gas, such asnitrogen. Most preferably, the heating means and the components arelocated in a hot zone defined by a heat shield within the chamber, toincrease heating efficiency. However, the heat shield should be arrangedto allow heating of the chamber walls to a temperature sufficient toavoid oil condensing on the walls.

Preferably also, the piping between the furnace and the pump isinclined, such that any condensate forming in the piping flows away fromthe furnace. In addition, or alternatively, the piping may be heated toa temperature sufficient to avoid or at least minimise condensation onthe piping.

The invention has particular application in de-oiling aluminium alloystrips, as used in the auto industry to form evaporators, radiators, airconditioners and the like, which have been contaminated with lubricatingoil from the presses used to form the strips. In this application it hasbeen found that, for safe and efficient operation of the system, it ispreferred that: the walls of the furnace chamber are maintained at above85° C.; the hot zone is defined by a single heat shield; the processpressure is less than 7×10⁻² mbar; the hot zone temperature is about350° C.; and the components, or furnace load, should be heated to about275° C. within fifteen minutes, which typically requires conditioning,or pre-heating, of the furnace.

These and other aspects of the present invention will now be described,by way of example, with reference to the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic representation of apparatus for use inde-oiling components, in accordance with a preferred embodiment of thepresent invention; and

FIG. 2 is a more detailed schematic representation of the apparatus ofFIG. 1.

Reference is first made to FIG. 1 of the drawings, which is adiagrammatic representation of apparatus for use in de-oiling componentsin accordance with a preferred embodiment of the present invention. Theapparatus includes a furnace 10 connected to three pumps 12, 14, 16 forpulling a vacuum in the furnace 10. In this particular example the firsttwo pumps 12, 14 are Roots blowers. The first pump 12 has a higherpumping capacity and one of the pumps 12, 14, in this example theintermediate pump 14, is provided with an electronic speed control toallow faster pump down and to permit the speed of the blower to bevaried in order to provide optimum matching of the Roots ratios. Thethird pump 16 is in the form of a two stage liquid ring pump 16. Intesting, a pump system comprising a 2,500 m³ /hr Roots blower 12, backedby a 1,800 m³ /hr Roots blower 14, in turn backed by a liquid ring pump16 with a displacement of 100 m³ /hr was found to be capable of reachinga pressure in the region of 2×10⁻² mbar.

The furnace 10 comprises a chamber 18 within which a single layer sheetof stainless steel 20 defines a hot zone 22. Within the hot zone 22 arethe heaters 24, in this example in the form of sealed Incoloy™ mineralinsulated heaters. All of the electrical connections for the heaters 24are provided outside the vacuum chamber 18 in order to reduce thepossibility of oil vapour being ignited by sparks. The components 26 tobe de-oiled are of course also located within the hot zone 22.

Reference is now also made to FIG. 2 of the drawings, from which it willbe noted that the exhaust from the liquid ring pump 16 is provided withan exhaust filter 27 in the form of a baffled chamber including a heatexchanger\condenser 28. Also shown in FIG. 2 is a cryogenic condenser 30provided between the first Roots blower 12 and the furnace 10. Thecondenser 30 removes a large proportion (up to 80%) of vapour from theair drawn from the furnace 10 but, as described below, is not consideredan essential feature of the apparatus.

FIG. 2 also illustrates the various sensors, inlets and outlets providedon the furnace 10. In particular, the furnace is provided with: anitrogen inlet 32; a capacitance manometer 34 for vacuum measurement, aBourdon gauge 36 for pressure measurement; a pressure relief valve 40; adrain 42 from the furnace chamber base; and temperature sensors for thehot zone 44, the heaters 46 and the components 48 located in thefurnace.

In use, oil-contaminated components, in this example aluminium alloyevaporators for use in forming automobile air-conditioning systems, arelocated into the conditioned, or pre-heated, furnace 10. The pumps 12,14, 16 are switched on and reduce the furnace pressure to less than7×10⁻² mbar. The hot zone 22 in the furnace is then heated to around350° C., with the components being heated to about 275° C. within aroundfifteen minutes. Also, the walls of the vacuum chamber 18 are heated toat least 85° C. to ensure that the oil vapour will not condense on thewalls.

Due to this pressure and temperature environment any oil contaminatingthe aluminium components evaporates and is drawn from the furnace 10.Depending on the configuration of the valves 48 around the cryogeniccondenser 30, the air drawn from the furnace either bypasses thecondenser or passes through the condenser, in which case around 80% ofthe oil vapour condenses therein any may subsequently be removed. Anyoil vapour remaining in the air passes through the Roots blowers 12, 14,without adversely affecting their operation, before passing through theliquid ring pump 16, the majority of the oil vapour remaining in the aircondensing in and around the pump 16. The pipework between the pump 16and the furnace 10 is inclined such that any condensate in the pipeworktends to drain towards the pump 16. Also, the piping between the furnace10 and the pump 16 is heated to minimise the possibility of suchcondensate forming.

The sealing oil in the pump 16 is selected to be compatible with the oilthat has been removed from the components such that mixing of the oilsdoes not adversely affect their operation of the pump 16. In most cases,the oil in the pump will be the same as the oil to be removed from thecomponents, for example Winsor Durel oil. Any excess oil is simply blownthrough the pump 16, or may be drained from the pump condenser.

At the end of the de-oiling cycle, which is likely to last for abouttwenty minutes, the chamber 18 is vented with nitrogen through the inlet34 to cool the heaters 24 and the components. Thus, when the furnacedoor 50 is opened the lowered temperatures will reduce the likelihood ofignition of any oil remaining in the furnace, which can result inexplosion.

It will be clear to those of skill in the art that the above-describedsystem obviates the difficulties encountered with oil contamination inconventional pump systems. Further, it is believed that the disclosedsystem will operate effectively without requiring provision of thecondenser 30, substantially reducing the costs associated with thede-oiling plant. Also, the disclosed furnace configuration has beenfound to allow the de-oiling process to be carried out satisfactorilywith relatively low power heaters and a much reduced risk of explosion.

It will also be clear to those of skill in the art that theabove-described embodiment is merely exemplary of the present invention,and that various modifications and improvements may be made theretowithout departing from the scope of the invention.

We claim:
 1. Apparatus for use in de-oiling components, the apparatuscomprising:a furnace for receiving components to be de-oiled; and meansfor creating a vacuum in the furnace, said means including a liquid ringpump, wherein oil is utilised to form the liquid ring and the oil isselected to be compatible with or the same as the oil to be removed fromthe components.
 2. The apparatus of claim 1 wherein a condenser isprovided on the exhaust of the liquid ring pump, to condense any oilvapour which passes through the pump.
 3. The apparatus of claim 1wherein said means includes also a lobed pump.
 4. The apparatus of claim3 wherein the lobed pump is in the form of a Roots blower.
 5. Theapparatus of claim 3 wherein a plurality of lobed pumps are provided,and at least one of the pumps is provided with means for varying thespeed thereof.
 6. The apparatus of claim 3 wherein the lobed pump isprovided between the liquid ring pump and the furnace.
 7. The apparatusof claim 3 wherein a plurality of lobed pumps are provided and arevertically spaced to minimise collection of condensate therebetween. 8.The apparatus of claim 1 wherein the furnace is provided with heatingmeans for heating the furnace the heating means being spaced from thewalls thereof.
 9. The apparatus of claim 8 wherein a heat shield definesa hot zone within the furnace for accommodating the heating means andthe components to be de-oiled.
 10. The apparatus of claim 9 wherein theheat shield is arranged to allow heating of the furnace walls to atemperature sufficient to avoid condensation of oil on the walls. 11.The apparatus of claim 1 wherein piping between the furnace and theliquid ring pump is inclined such that any condensate forming in thepiping flows away from the furnace.
 12. The apparatus of claim 1 whereinpiping between the furnace and the liquid ring pump is provided withheating means for heating the piping to a temperature sufficient toavoid or at least minimise condensation on the piping.
 13. A method ofde-oiling contaminated components, the method comprising thesteps:heating the oil-contaminated components in a furnace; pulling avacuum in the furnace, the vacuum being created using a liquid ring pumputilising oil to form the liquid ring, and the oil utilised to form theliquid ring is selected for compatibility with the oil to be removedfrom the components.
 14. The method of claim 13 wherein the furnace andthe components therein are cooled by venting the furnace chamber at theend of a de-oiling cycle.
 15. The method of claim 14 wherein the furnacechamber is vented with an inert gas.
 16. The method of claim 13 whereinthe walls of the furnace are heated to a temperature sufficient to avoidcondensation on the walls.
 17. Apparatus for de-oiling components, theapparatus comprising:a furnace for receiving and heating components tobe de-oiled; means for creating a vacuum in the furnace and drawingvaporized oil from the furnace, said means including a liquid ring pump,wherein oil is utilised to form the liquid ring and the oil is selectedto be compatible with or the same as the oil to be removed from thecomponents; and a condenser upstream of the liquid ring pump forremoving a proportion of the vaporized oil drawn from the furnace.
 18. Amethod of de-oiling contaminated components, the method comprising thesteps of:heating oil-contaminated components in a furnace; pulling avacuum in the furnace, to vaporize the oil, using a liquid ring pumputilising oil to form the liquid ring, the liquid ring oil beingselected for compatibility with the oil to be removed from thecomponents; drawing the vaporized oil from the furnace; and condensing aproportion of the vaporized oil in a condenser located upstream of theliquid ring pump.
 19. Apparatus for de-oiling components, the apparatuscomprising:a furnace for receiving and heating components to bede-oiled; means for creating a vacuum of at least 7×10⁻² mbar in thefurnace and drawing vaporized oil from the furnace, said means includinga liquid ring pump, wherein oil is utilised to form the liquid ring andthe oil is selected to be compatible with or the same as the oil to beremoved from the components; and a condenser upstream of the liquid ringpump for removing a proportion of the vaporized oil drawn from thefurnace.